The invention relates to apparatus for extending a line in a fluid medium, and more particularly to a sonobuoy having hydrophones deployable in a linear array at a selected depth.
Line arrays of hydrophones are particularly useful for localizing the source of acoustic signals at long range because of their ability to listen with improved signal-to-noise ratio along narrow beams transverse to the arrays. It is especially important to maintain the array straight for optimum beam pattern.
Various devices have been used to deploy the line array. In one system, disclosed in U.S. Pat. No. 3,944,964to Loeser et al, the array is stretched between a sea anchor and a surface float. In variable winds and currents, the array many bend, and degrade the beam pattern. In addition, its direction is limited by the directions of the wind and current. Another device, disclosed in U.S. Pat. No. 4,004,265to Woodruff et al, an electric or compressed gas thruster stretches the line array in any desired direction from a sea anchor. The thruster uses an electrical or compressed gas power source with a water or gas jet, or an external propeller. While these thrusters operate independently of the magnitude and direction of wind and currents, they generally have low energy-to-weight ratios which discourage their use in air-launched sonobuoys, such as the Navy's standard A-size. Thrusters having higher energy-to-weight ratios suitable for sonobuoys usually generate noise in a frequency band which interferes with receiving by the hydrophone array.
Accordingly, it is an object of the present invention to provide an improved system for extending a line in a fluid medium. Another object is to provide a sonobuoy with an improved thruster capable of rapid-powered deployment of a linear array of hydrophones and of continuous duty for maintaining linearity over the designed operating life of the sonobuoy. A further object is to provide a thruster for a hydrophone line array which generates low-level noise in a frequency band which does not interfere with the performance of the receiving array of hydrophones. Still another object is to provide an expendable thrust device which is small, relatively inexpensive to manufacture, and which is safe to store, use and maintain.
Briefly, these and other objects of the invention are accomplished by a sonobuoy having a line of hydrophones deployable in the water in a linear array by a metal hydride jet thruster. The thruster is powered by releasing hydrogen gas from a metal hydride material and igniting the gas in a mixture with oxygen to produce an in-water thrust required for extending the array.
For a better understanding of these and other objects and aspects of the invention, reference may be made to the following detailed description wherein: